Hearing aid device



March 5, 1940. A, M WENGEL HEARING AID DEVICE l 2 Sheets-Sheet 1 Filed March 6. 1957 March 5, 194% A: M. WENGEL.

HEARINGYAID DEVIQF Filed March 6, 1957 ,2 Sheets-Sheet 2 vPatented 5, 1940` l 2,192,669 l UNITED- STATES PATENT OFFICE i v '2,192,669A l l t Y HEARING AID DEVICE Arthur ltwengel, Madison, Wis., assignor to Ray-(l-vac Company, a corporation of Wis- Application March 6`, 1937,Serlal No.` 1294,51v4' o nomma. (ol. 179-101) l i u invention is .that the overtones *3T-Sounds in 1911e erly inthe patients ear; and any intensity above higheraudible frequencies are accentuated; anthe maximum causes pam and such jumbung of other feature is that standard sets for stock purthe sounds as to render understanding difdcult. DOSeS me? be manufactured end then Slightly The present device incorporates -automatic voladded t0', t0 meet the requirements 0f apartieuler ume control means so that the intensity of the 2li deneent eef? e further feature iS the nlevieien 0f sound transmittedto the usersear is maintained 20 automatic control means for maintaining. the constant despite variations mme input to the output of said device substantially constant dedevice spite Variations in the input; another feature ie The automatic volume control operates in conthe use of ahigh gain-audO amplier- Other feejunction with an audio amplier having a relatures and eovantege-s of invention Wm -be tively high over-all gain. 'I'his enables relatively 2 5 apparent@ the following specification and the weak sounds, such as whispers or voices located dra'Wingsi-m which: at a considerable distance from the microphone Figure 1 is o front elevation of e heering eid input to thedevice to be amplied suillciently to .c device embodying thisinvention: F18. 2 isa side fau with1n-the desired audibmty range for the w elevation, partly in section, of the deviceshown heali ,in Fis- 1: Fia 3 is a Schematic dimm Gf the In thc usual type cf hearing cid device the device; Fig. 4 is a sectional view of the microuse of a high gain'audio amplifier would re phone? Fig- 5 is a View along the une o o of sult in an impractical device, since microphonic Flg- 41 and F18. 6 iS e View 0f e lnndined tone noises generated in the usual carbon microphone 3o control oiroult' .f by vibration would be so amplified as to greatly 35 It has' been mund that the ear '0f a dee! perdisturb thc-user. This device overcomes this and son is generally more dencient with respect t0 other difiiculties ,by employing a crystal mcrocertain. audible frequencies than With l'eepeet to phone. vThe crystal microphone isk not only free 'othere That is the deaf Person'e eel' me! have from intergranular scratching sounds found in a' fairly goed response for frequencies in the carbon microphones, but has a very good re- 40 lower range, and be very defeeve with reepeet spouse to all frequencies within the audible range. to those in the higher range. In such a case it It has been mund that m the majority of cases .is Very dimoult for that person to distinguish-ben of deafness the patients ear is more deficient tween various .words which depend upon over' with respect tothe higher frequencies than the 45 me or higher tone quality to differentiate them lower. In the general run of cases, therefore,

from other words' The present invention 'pm'. it is preferable to pick up .and amplify the tones vides a hearing aid device which can be adjusted of higher frequency more than those'in the lower to the needs of the particular user or patient band. It has beenv found that crystal microand which Vwill amplify the higher frequencies, phones can be designed with rising frequency for example in a ratio wmch justneutrauzes thecharacteristic,V so that their output 'contains a 50 deciencies' of the patients ear' This results' higherl proportionof the higherfrequenoies than orcgmse' in' the patients reiviegsiamdtom existed in the sound waves energizing them. i?? which affects mm m e Such a microphone enables subsequent tone cony. o trol features in the amplier to be effective to u This invention relates to a hearing aid device, and more particularly to a device intended to accentuate certain audible frequencies more than others. I

Oney feature lof this invention is that it is a very efllcient hearing aid device; another fea ture of jthis invention is that it furnishes a deaf person withaudible sounds which affect his ear insucha way as to give a normal tone pattern; yet another feature of this invention isthat it accentuates the frequencies to which the ear of the heater has a deficient response; a. further feature of this invention is that microphonic noises are eliminated; still another feature of this In certain cases ithasbeenfcundthatthe ear is more' dencient with respect to low tones than to high, or the response may be good to both low and high tones and deficient with rethe minimum will not, of course, register prop- The device disclosed 5 their full extent, since the higher tones are not lost in the microphone.

In the particular embodiment of this invention disclosed herewith, a hearing aid device I 0 comprises a relatively small light carrying case II of leather or the like, having therein a microphone-amplifier unit I2 and batteries I3 and I4 for energizing the device. The batteries are readily removable for replacement purposes, and are operatably connected to the unit I2 by wires I5 which make connection therewith throughjacks plugged into sockets in the top of the battery cases. The microphone I6 is positioned behind an opening I1 through which sounds are transmitted to it for subsequent amplification and reproduction. Beneath the microphone opening is a knob I9 which acts as a switch and volume control which may be set by the patient in accordance with his wishes. At the lower part of this same end of -the device sockets 20 are provided adapted to receive the tips of a flexible cord leading to a conventional receiver or bone conduction device worn by the patient. This forms no part of the present invention and is not illustrated herewith.

Referring more particularly to Fig. 3, it will be seen that the device comprises a crystal-microphone I6, a high gain audio amplifier, an output here shown as a receiver 2|. an automatic volume control circuit, and two independent tonel controls 22 and 23.

The amplifier is here shown as comprising tubes 24', 25 and 26, at least two of thetubes, here shown as 24 and 26, being screen grid tubes with a high amplification factor. Just prior to the input to the tube 26 part of the currents passing through the amplifier is diverted by the lead 21,

amplified in the tube 28, rectified in the tube 29 and the resultant direct current voltage is applied through the wir'e 30 to the grid or input circuit of the tube 24 to control the amplification factor thereof.

The tone control means 22 comprises a reactance element or condenser 3|, a. variable resistance 32, and a path 33 to ground. Since a condenser inherently passes high frequency currents and offers considerable impedance to low frequency currents, the tone control 22 provides means whereby high frequencies may be removed and dissipated to ground. The proportion thus removed'is contrclled by the variable resistance 32. A'I'he tone control 23 comprises a variable resistance 34, another reactance element here shown as an inductance 35, and a path 36 to ground. -The inductance ls here illustrated as of the ironcore type, and imposes high impedance to high frequencies while easily passing low frequencies. Thus the tone control 23 provides an adjustable path through which a desired proportion of the low frequencies may be dissipated to ground. The general audibility level or volume control actuated by the` knob I9 is here shown as the variable resistance 31.

The alternating current voltage developed by Vibrations ofthe crystal 31 inthe microphone I6 is developed across resistor 38 of one or two megohms and impressed upon the grid of the tube 24. `The output from the plate of this tube 24 is impressed through the blocking condenser 39 of about one-tenth m. f. on the ,wire 4,0. The coupling is of the resistance type through a resistor 4| here having about 250 m. impedance. The amplified current impressed on theA wire 40 has three possible paths: one is through the tone control circuit 22 through which the desired amount of high frequencies may be dissipated; another is through the tone control circuit 23 through which low frequencies may be dissipated; and the third is to the volume control or variable resistor 31, from which a desired amount is impressed on the grid'of the succeeding tube 25. The plate output of this tube is in turn coupled, through the plate load resistor 42 and the' blocking condenser 43 on the grid of the tube 26, also a screen grid high gain tube similar to 24. The output pf this tube is developed across the ear piece or receiver 2| in order that sounds received by the microphone I6 and translated into electrical impulses may be transformed again into sound Waves to affect the ear of the patient. Between the blocking condenser 43 and the grid of the tube 26, the wire 21 diverts part of the currents flowing through the amplifier, and impresses voltage developed across the variable resistor 44v on the grid of the tube 28, which is in turn resistance coupled to the rectifier 29.

This rectifier tube develops a vdirect current drop across the resistor 45, which is appliedv through the filtering resistor 46 andthe wire to-the grid circuit of the tube 24. The'blas or potential of the grid of the tube 24 with respect to ground is, therefore, a function of the potential drop across the resistor 45, which is in turn a function of the amount of current in the amplifier. A large input to the tube 24, as a result of shouting or speaking too close to the microphone of the device, thus automatically operates to reduce the amplification factor of the tube 24 and maintain the output of the amplifier developed in the receiver 2| at substantially constant intensity. It Will be noted that a battery 41 maintains the filament of the rectifier tube 29 at a positive potential with respect to ground. This prevents operation of the automatic volume control portion of the circuit until the plates of the tube 29 have swung positive with respect to the filament, and thus there is a delay action which maintains the sensitivity of the amplifier at its highest level until the desired intensity for the particular hearer is reached, whereupon the volume control circuit maintains that desired intensity. The tubes are, of course, of the type particularly designed for use with batteries in order to prevent an excessive battery drain. The tube 24, for example, may be a 1-B4, the tube 25 a '30, and 26 a 1-F4. Any other tubes suitable for such a device may, of course, be substituted with the necessary changes in circuit constants.

In the commercial device the resistors 32, 34

` and 44 are not variable by the patient, but are set at the factory or other place where the device may be purchased. For production purposes a standard device is produced which does not have either the tone control circuit 22 or 23 therein. It is merely a high gain audio amplifier, either with or without the automatic volume control circuit, appropriately connected to the microphone,. batteries, and receiver. The particular patient foi' whom the device is intended is tested for frequency responses, and both the minimum level of audibility and the level at which pain is produced are determined for a number of frequencies throughout'the audible range. A chart or curve is then plotted which shows the response pattern of the particular patient. Let us assume that the response is half normal for-the low frequencies and drops steadily towards the higher frequencies with a slope of about 20, so that these higher frequencies are not heard anywhere near as well' as the lower ones. 'Ihe reactance n funest.

element comprising the tone control circuit 28 would then be inserted in the standard production device and a resistance value chosen which is known to taper oi! or dissipate the low fre- 6 quencies at a slope of about 20. This would result in the iinished amplifier having a rising am pliiication characteristic; inother words, the amplification of the high frequencies would increase in proportion to the frequencies with a slope of about In the particular case of deafness described above, which is fairly common, the tone control portion 22 would not be` necessary. Thus, the finished device would amplify the higher frequencies more than the lower ones by the proportion in which the patients ear is deficient thereto, so that the final audibility pattern heard by the patient would be normal, with both high and low frequencies having lthe proper apparent' relationship to each other.

sible combinations of one or both of the tone control circuits 22 and 23, would be available to provide an amplihcation curve adapted to coxnpensate for the deiicienciesof each particular patient. Ln order to be most effective, of course, the device must be completed in accordance with a prescription or chart developed from a thorough test of the patients hearing response at variousfrequencies. Inasmuch as the majority' of cases of deafness are deficient in response to the higher frequencies, the crystal microphone I6 is so chosen and designed as to have a rising frequency characteristic in order to rnake these high frequencies available. In other words,`the electrical output of the crystal microphone containsia higher proportion of the higher frequencies than'the sound input thereto. The advantages o'f the high gain amplifier and the tone control circuits may thusv be realized'to their The crystal microphone has two very great advantages over the usual carbon granule microphone used inV such a device. One of these is the fact' that high frequencies may be available for subsequent amplification, which is not possible with the usual carbon microphone; and theother is that intergranular noises resulting from vibration of the usual carbon microphone are completely eliminated, with highly satisfactory results from the patients standpoint. I0 The particular microphone usedin connection with thisv hearing aid is illustrated in Figs. 4 and 5. The crystal 31 is diamond shape and ilxedly mounted at one corner Il in the stand 52. The driving diaphragm or cone I6 is fastened to the casing 52 around its circumference, and operatively connected at its apex to one corner of the crystal 31 bythe connecting means 53'. Flexible electrical conductive elements 54l and i! on'each side of the crystal serve to take o the alternatl0 ing currents generated by mechanical vibration of the crystal. ".I'hese two elements are connected by the leads 56 and 51, respectively, to outlet terminals 58 and 59 projecting outside of the case and furnishing terminals by which the mi- 65 Icrophone may be connected in the circuit.

Where the pain level of the patient is rather close to the minimum audibility level, or where the ability to understand a 'differential between sounds is destroyed by too great an intensity, the

70 automatic volume control portion of the circuit insures the desired intensity regardless of changes in the sound level with respect to the microphone or input of the device. The amount of volume control action desired may be regulated by variable resistor u and the threshold at which its aisance Other combinations of settings, including all pos- 1- action commences by the delay voltage tl. The use of the amplifying tube 28 ahead of the rectifying tube enables suillcient control voltage to be developed to meet'all conditions. Where the output does not have to be maintained exactly con stant or the variations in the input are not expected to be too great, this amplifying tube may be eliminated.

Another or modied form of the tone control portion o f the circuit is illustrated in Fig. 6. The tubesj and 6i correspond to the tubes 24 and 25, respectively, in the circuit illustrated in full in Fig. 3. In this form, however, the plate circuit of tube 60 is coupled to the input or grid circuit of tube 6I by tlie transformer 62. Again three paths are provided from the point 63 on for currents iiowing in the plate circuit of the tube 60; one path is through the transformer 62; another path Vis through the reactance element or condenser and the variable resistance 65 to ground; and the other path .is through the condenser 66 and variable resistance 61 directly to the grid of the tube 6I. The condenser 64 and variable'resistance 65 provide means for dissipating a desiredlproportion of the high frequencies to ground, and thus accentuating the lows. The condenser i6, and variable resistance 61 provide means for directly coupling the plate of the tube 60 to the grid of the tube 6i, so that a desired larger pro' portion of high frequencies may be passed to the grid to accentuate these frequencies in the inal output of the device. While I have-described and claimed certain embodiments of my invention it is to be understood that it is capable of many modications. Changes therefore' in the construction and arrangement 'maybe made without departing from the spirit and scope of :the invention as disclosed in the l l appended claims in which it is my intention to claim all novelty inherent in my. invention as broadly as permssiblein view of the prior art.

I claim: l f

l. A hearing aid device of the character described, including: a relatively small, light case adapted for convenient carrying; a microphone so mounted in said case as to be readily energized by sound waves, said microphone including a piezoelectric crystal for translating sound waves into electrical impulses; a battery; an amplifier conriected'to said microphone,- said ammeans for translating said impulsesback into l' sound waves. 'v y I 3. In a hearing aid devicefof the character described for apatient having a more deficient response to certain frequencies than to others in the audible range: a crystal microphone for translating sound waves into electrical impulses; an amplifier for amplifying said impulses, said amplifier-having at least two tubes and being so constructed and arranged as to amplify thev frequencies to which the patient is defective more pliiler having vthe operating currents therefor than the other frequencies in the audible range: and receiver means for translating said impulses back into sound waves.

4. In a hearing aid.- device of the character described for a particular patient: a crystal microphone for translating sound waves into electric-al impulses; means for amplifying said electrical impulses, said amplifying means including tone control means for dssipating the frequencies to which the patient is most responsive; and receiver means for translating said impulses back into sound waves.

5. In a hearing aid device of the character described for a particular patient: a crystal mic-rophone for translating sound waves into electrical impulses; means for amplifying said electrical impulses, said means including at least two tubes having high amplification factors and operative circuit connections therefor; receiver means for translating said impulses back into sound waves; means in said circuit between said l'ubes for regulating the proportion of high frequency impulses passing to said second tube; and a second means in said circuit between said tubes for regulating the proportion of low frequency impulses, at least one of said two last mentioned means dissipating a portion of said impulses.

6. In a portable hearing aid device of the character described: microphone means for translating sound waves into electrical impulses; means for amplifying said impulses; receiver means for translating said impulses back into sound waves; and means for maintaining the output' oi said amplifier substantially constant despite variations in the intensity of said sound waves.

7. In a portable hearing aid device of the character described: microphone means for translatingl sound waves into electrical impulses; means for amplifying said impulses, said means including at least two tubes having a high amplification factor and operative circuit connections therefor; receiver means for translating said amplied impulses back into sound waves; and means for maintaining the output of said amplifier substantially constant despite variations in the intensity of the sound waves entering said microphone, said means diverting a portion of said 'impulses in said circuit prior to the last of said tubes.

8. A portable hearing aid device of the character described, including: an audio frequency amplifier comprising at least two tubes having a grid, cathode and plate each, operative circuit connections for said tubes and input and output connections for said amplifier; a microphone connected to said input for translating sound waves into audio frequency currents in said circuit; receiver means connected to said output for translating said audio frequency currents back into sound waves; and means for controlling the amplification characteristic of the first of said tubes, whereby the outputof said amplifier is maintained substantially constant despite variations in the input thereto, said means diverting a part of said current in said circuit prior to said output, rectifying said diverted current and impressing it on the grid of said first tube. f

9. Apparatus of the character claimed in claim 8, including means for delaying the action ofsaid volume control means until a predetermineddesired output has been attained.

10. A hearing aid device of the character described, including: a relatively small, light case adapted for convenient carrying; `a small, sensitive crystal microphone, for translating 1sound waves into electrical impulses, mounted in the case; and an amplifier in the case, the amplifier including at least two tubes and being adapted to highly amplify the electrical impulses from the microphone; and a receiver connected to the amplifier and adapted to be worn bn a defective ear, whereby the sound waves energizing the microphone are transmitted' in amplified volume to the ear.

1l. A portable hearing aid device of the character described for delivering amplified sound impulses to a receiver worn on a defective ear, including: microphone means for translating sound waves into electrical impulses; amplifying means, including at least two tubes, for highly amplifying'the electrical impulses from the microphone and delivering themI to the receiver; and means for maintaining the intensity of the impulses delivered to the receiver substantially constant despite variations in the intensity of the sound waves actuating the microphone means.

AR'I'HUR M. WENGEL. 

